1. Field of the Invention
The present invention relates to a drive mechanism for driving a movable mirror provided in a camera (e.g., an SLR camera), and in particular to a shock-absorbing mechanism, provided in association with the drive mechanism, for the movable mirror.
2. Description of the Related Art
In SLR cameras, a movable mirror (quick-return mirror) is provided, which is capable of moving up and down; more specifically, capable of rotating between a viewfinder light-guiding position (mirror-down position), in which the movable mirror is positioned in a photographing optical path to reflect incident light emanated from an object (object-emanated light) toward a viewfinder optical system, and a retracted position (mirror-up position), in which the movable mirror is retracted from the photographing optical path to allow the object-emanated light to travel toward a shutter. If the movable mirror bounces (vibrates) due to shock caused upon reaching a rotational limit position such as the viewfinder light-guiding position or the retracted position, this bouncing of the movable mirror makes the image that is viewed through the viewfinder unstable, causing an adverse effect on the viewing performance of the viewfinder. Additionally, in a camera which is structured to lead light from an object to a distance measuring sensor and a photometering sensor via a movable mirror, a precise distance measuring operation or photometering operation cannot be performed during such bouncing of the movable mirror, which restricts continuous photographing performance. Due to such reasons, various shock-absorbing mechanisms which absorb shock of the movable mirror when it rotates to suppress bounce of the movable mirror have been proposed (e.g., Japanese Unexamined Patent Publication No. 2000-131755).
Movable mirror shock-absorbing mechanisms are provided with shock-absorbing members which are pressed by a movable mirror during rotation thereof. The shock-absorbing members absorb the momentum of the movable mirror by applying a load against pressing movement of the movable mirror. The mirror-down position and the mirror-up position, which correspond to rotational limit positions of the movable mirror, are determined by two stoppers, respectively, which are fixed to a mirror box that accommodates the movable mirror. However, if the contact engagement between the movable mirror and a shock-absorbing member is maintained with the movable mirror having reached either rotational limit thereof, there is a possibility of the shock-absorbing member interfering with the positioning of the movable mirror that is determined by the associated stopper. Accordingly, at each rotational limit of the movable mirror, where the movable mirror comes in contact with the associated stopper, it is desirable that the engagement of the movable mirror with the associated shock-absorbing member be released. More specifically, the following measures have been taken: the range of movement of the shock-absorbing member(s) is made to include an overrun range which exceeds a shock-absorbing moving range in which the shock-absorbing member comes into contact with and is pressed and moved by the movable mirror, and the shock-absorbing member is held in the overrun range when the movable mirror reaches the associated rotational limit.
However, as the speed of rotation of the movable mirror is increased to improve a continuous photographing capability, the motion energy of the movable mirror increases, so that a problem arises with already-existing shock-absorbing members not being able to sufficiently reduce bounce of the movable mirror. More specifically, if loads of the shock-absorbing members on the movable mirror are excessively increased to enhance the bounce suppressing effect, there is a possibility of the load on the mechanism for driving the movable mirror excessively increasing or the operational speed of the movable mirror during rotation thereof decreasing. On the other hand, if loads of the shock-absorbing members on the movable mirror are excessively small, motion energy of the movable mirror cannot sufficiently be absorbed, which makes it impossible to prevent the movable mirror from bouncing upon the movable mirror reaching a rotational limit thereof. Accordingly, there has been a problem with it being difficult to set shock-absorbing members for effectively preventing the movable mirror from bouncing without deteriorating the drive performance of the movable mirror.